I have been happy with the results I have been getting with new version of the Spectrum Analyzer interface board. Unfortunately now I am waiting on the new si5351 board I want to use. Looking around for something to do I came across the BITX-40 board by Asher Farhan. This is a single board version of his BITX design, and is being produced by a collective of local women in their homes to provide a livelihood.
More information including schematic and a great circuit description is available at http://www.hfsigs.com/
I had previously started a modular version of the BITX, but this looked like would make a nice small portable transcever.
This board is only available in India, so if I wanted one I would have to build one for myself. I decided to layout a board using using SMD components. Although I am using SMD components, I will keep the board size about the same as the original. Since I will be using a home made PCB without a solder mask I used 1206 size components and allowed plenty of space around each component. Without a solder mask it is very easy to have problems with solder bridges with SMD components. I also made it a double sided board, with the the DC power lines on the bottom of the board. Unlike the original, I did not include the VFO and BFO circuitry. I plan on using a si5351 much like the one I built for the Canned Frog. 
Because of the size of the board I could not use the free version of EAGLE that I have been using. There are several other free PCB design software packages around, but I had some experience using ExpressPCB. There is not a large component library as available for EAGLE, but it is fairly easy to add custom components to the ExpressPCB library. The other issue with ExpressPCB is that it is designed to be used with the ExpressPCB board service, so there is no provision for generating Gerber files if you want to use a different board service. One of the other PCB software packages I had tried was Copper Connection. It was fairly easy to use, but I preferred ExpressPCB. One of the things Copper Connection can do is read ExpressPCB files and then generate Gerber files. It also has a very easy way to print the bottom and mirrored top copper layer for use with toner transfer at one time. So I will use ExpressPCB to layout the board, and export that to Copper Connection to print the toner transfer images.After I finished the layout, I tried to make a board. I have had very good luck using the Cold Toner Transfer method, But because of the board size, the clamping fixture use would not cover the whole board, and I ended up with areas on the board where the toner did not adhere to the copper.
I tried using the Hot method with my laminator, but could not get the toner to stick to the copper at all. As a last resort I processed a board with the Cold method solvent, and instead of using the clamping fixture I fed it through the laminator without waiting for it to heat up. I ran it through a couple more times as it was warming up and when I checked the board and it was nearly perfect. I had to touch up a few pinholes in large copper pours, but all the traces were perfect. I got the board etched and now to start building the board. 
nice board. wish you good success in managing it work.
ReplyDeleteI like all your projects DuWayne. I am thinking about using your BITX layout and do it in CirCad. I been using CirCad for some time now, bought a copy of it since I do some free lance layout work for mad money from time to time. You have great Blog. John kg9dk
ReplyDeleteWhen I finish building the xcvr and get every thing checked out I will publish the board files so others can build one. So far I have only found one very minor error on the first board, and see a couple of changes I want to make.
DeleteHi DuWayne:
ReplyDeleteI am inrerested building the BIT40 xcvr and was wondering if you have publised the board files yet.
Thanks Ross K7RSB
Still building and testing, will post files when finished.
ReplyDeleteDuWayne
did you succeed ? share your files :)
ReplyDeleteI stated in one of my later posts, that when the SMD version of the BITX40 became available I decided to just buy one of them instead of completing my own version. The one I started on is still unfinished, and I had found a couple things I needed to change so it just sits until I finish several other projects.
ReplyDeleteSir please give me a layout & details
ReplyDeletehello can you share the pcb files?
ReplyDeletePlease sir can you share the pcb files?
ReplyDeleteyou mentioned you used the cold method for this board and then fed it through the laminator instead of applying pressure. Would you consider this best practice? Apply solvent mixture, let rest for 30 secs, run through cold laminator a few times?
ReplyDeleteWhat has worked best for me was to start with the laminator cold as it is warming up, Run through from a different direction each time This seems to give an even transfer over all of larger boards, epically if there is a large ground plane area
ReplyDelete